From 4cc05543d48a35908b0756e133bd668745bd95c3 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@ost.ch>
Date: Sun, 26 Jul 2026 13:23:46 +0200
Subject: kapi: implement device removal

---
 kapi/kapi/devices/device_registry.hpp   | 30 ++++++++++++
 kernel/kapi/devices/device_registry.cpp | 82 ++++++++++++++++++++++++++++++---
 2 files changed, 106 insertions(+), 6 deletions(-)

diff --git a/kapi/kapi/devices/device_registry.hpp b/kapi/kapi/devices/device_registry.hpp
index 3952db66..a65bd4ad 100644
--- a/kapi/kapi/devices/device_registry.hpp
+++ b/kapi/kapi/devices/device_registry.hpp
@@ -18,12 +18,36 @@ namespace kapi::devices
   //! @addtogroup kapi-devices-kernel-defined
   //! @{
 
+  //! The interface for types interested in being notified about changes in the device registry.
+  struct device_registry_observer
+  {
+    //! Enable correct destruction through base pointers.
+    virtual ~device_registry_observer() = default;
+
+    //! Called after a device has been added to the registry.
+    //!
+    //! @param device The device that was added.
+    virtual auto on_device_added(kstd::shared_ptr<device> const & device) -> void = 0;
+
+    //! Called after a device has been removed from the registry.
+    //!
+    //! @param device The device that was remove.
+    virtual auto on_device_removed(device & device) -> void = 0;
+  };
+
+  //! @}
+
+  //! @addtogroup kapi-devices-kernel-defined
+  //! @{
+
   struct device_registry
   {
     device_registry() = default;
 
+    //! Initialize the global singleton registry instance.
     auto static init() -> void;
 
+    //! Get the global singleton registry instance.
     auto static get() -> device_registry &;
 
     //! Add a new device to the kernel's device registry.
@@ -49,8 +73,14 @@ namespace kapi::devices
     //! @return every device current reachable through the registry.
     [[nodiscard]] auto all() const -> kstd::vector<kstd::shared_ptr<device>>;
 
+    //! Subscribe to device registry notifications.
+    //!
+    //! @param observer The observer to notify.
+    auto subscribe(kstd::weak_ptr<device_registry_observer> observer) -> void;
+
   private:
     kstd::flat_map<kstd::string, kstd::weak_ptr<device>> m_devices{};
+    kstd::vector<kstd::weak_ptr<device_registry_observer>> m_observers{};
   };
 
   //! @}
diff --git a/kernel/kapi/devices/device_registry.cpp b/kernel/kapi/devices/device_registry.cpp
index aca0e7fe..f5c20a6d 100644
--- a/kernel/kapi/devices/device_registry.cpp
+++ b/kernel/kapi/devices/device_registry.cpp
@@ -49,29 +49,89 @@ namespace kapi::devices
 
     kstd::println("[OS:DEV] Registering device {}", device->name());
 
+    auto added = false;
+
+    // TODO: lock the registry
     auto found = m_devices.find(device->name());
     if (found != m_devices.end())
     {
       if (!found->second.expired())
       {
-        return false;
+        added = false;
       }
 
       found->second = device;
-      return true;
+      added = true;
+    }
+    else
+    {
+      added = m_devices.emplace(device->name(), device).second;
+    }
+    // TODO: unlock registry
+
+    if (!added)
+    {
+      return false;
     }
 
-    return m_devices.emplace(device->name(), device).second;
+    // TODO: consider if we need to lock the registry observers here, since somebody may add an observer in the meantime
+    // once multiple codepaths can run at the same time.
+    for (auto const & observer : m_observers)
+    {
+      if (auto locked_observer = observer.lock())
+      {
+        locked_observer->on_device_added(device);
+      }
+    }
+
+    // TODO: lock registry
+    erase_if(m_observers, [](auto const & observer) { return observer.expired(); });
+    // TODO: unlock registry
+
+    return true;
   }
 
-  auto device_registry::remove(device &) -> bool
+  auto device_registry::remove(device & device) -> bool
   {
-    kstd::println("[OS:DEV] TODO: implement device deregistration");
-    return false;
+    // TODO: lock registry
+
+    auto found = m_devices.find(device.name());
+    if (found == m_devices.end())
+    {
+      return false;
+    }
+
+    auto locked = found->second.lock();
+    if (!locked || locked.get() != &device)
+    {
+      return false;
+    }
+
+    found->second = kstd::weak_ptr<struct device>{};
+
+    // TODO: unlock registry
+
+    kstd::println("[OS:DEV] Unregistering device {}", device.name());
+
+    for (auto const & observer : m_observers)
+    {
+      if (auto locked_observer = observer.lock())
+      {
+        locked_observer->on_device_removed(device);
+      }
+    }
+
+    // TODO: lock registry
+    erase_if(m_observers, [](auto const & observer) { return observer.expired(); });
+    // TODO: unlock registry
+
+    return true;
   }
 
   auto device_registry::find(std::string_view name) const -> kstd::shared_ptr<device>
   {
+    // TODO: lock registry
+
     auto found = m_devices.find(kstd::string{name});
     if (found == m_devices.end())
     {
@@ -83,6 +143,8 @@ namespace kapi::devices
 
   auto device_registry::all() const -> kstd::vector<kstd::shared_ptr<device>>
   {
+    // TODO: lock registry
+
     auto result = kstd::vector<kstd::shared_ptr<device>>{};
 
     for (auto const & [name, weak_device] : m_devices)
@@ -95,6 +157,14 @@ namespace kapi::devices
 
     return result;
   }
+
+  auto device_registry::subscribe(kstd::weak_ptr<device_registry_observer> observer) -> void
+  {
+    // TODO: lock registry
+
+    erase_if(m_observers, [](auto const & observer) { return observer.expired(); });
+    m_observers.push_back(observer);
+  }
 }  // namespace kapi::devices
 
 namespace kapi::test_support::devices
-- 
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